I. Field of the Invention
The present invention relates to multicarrier spread spectrum communications.
II. Description of the Related Art
OFDM has a high spectral efficiency (the spectrum of the subcarriers overlap) and combats frequency-selective fading. However, the amplitude of each carrier is affected by the Rayleigh law, hence flat fading occurs. Even with good channel estimation and channel coding, fading and interference can easily compromise the performance of OFDM.
Multi-carrier CDMA (MC-CDMA) applies CDMA spreading codes to orthogonal subcarriers to enhance frequency-diversity benefits. However, MC-CDMA, like OFDM, suffers from a high peak-to-average-power ratio (PAPR). The high PAPR of conventional multi-carrier signals imposes significant constraints on the transmission circuitry and significantly increases power consumption.
Carrier Interferometry (CI) is a multi-carrier technology invented by Applicant and described in over 70 technical journals and conference proceedings, as well as in two textbooks. As a multicarrier transmission protocol, CI provides unsurpassed performance and versatility compared to all other technologies.
There is a need in the art to employ frequency-diversity advantages on the sub-carrier level of a multicarrier signal. Also, there are acknowledged needs in the art for improved transmission security, enhanced channel coding, and dynamic-range reduction in multicarrier transmissions. Such needs are addressed by the present invention.